<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>控制样式</title>
    <style>
        .d1{
            border: 1px solid red;
            width: 100px;
            height: 100px;
        }
        .d2{
            border: 1px solid blue;
            width: 200px;
            height: 200px;
        }
    </style>
</head>


<body>
    <div id="div1">
        div1
    </div>

    <div id="div2">
        div2
    </div>
<script>
    let div1 = document.getElementById("div1");
    div1.onclick = function () {
        // 修改样式1
        div1.style.border = "1px solid red";
        div1.style.width = "150px";

        // font-size
        div1.style.fontSize = "20px";
    }

    let div2 = document.getElementById("div2");
    div2.onclick = function () {
        div2.className = "d1";
    }
</script>
</body>
</html>